Method of initiating the combustion of liquid hydrocarbon fuels



April 12, 1960 w. P. TER HORST METHOD OF INITIATING THE COMBUSTION OFLIQUID HYDROCARBON FUELS Filed Sept. 12, 1955 ATTORN EYS lating the flowof oxidizer and fuel.

United States Patent NIETHOD OF INITIATING THE COMBUSTION 0F LIQUID HYDROCARBON FUELS William P. Ter Horst, McDonogh, Md., assignor to OlinMathieson Chemical Corporation, a corporation of a Application September12, 1955, Serial No. 533,706 9 Claims. (Cl. 60-35.4)

. abandoned.

The principal elements of bi-propellent rocket motors :of the type nowin use for rocket propulsion or to give an accelerated take-off oraccelerated speeds to airplanes .utilize a liquid oxidizer and a liquidfuel and comprise a suitable housing, a combustion chamber, an exhaustnozzle, a propellent injection system including inlet orifices for fueland oxidizer and suitable control valves for regu- The combustionchamber can be provided with a cooling system, for example, a jacketthrough which the fuel is pumped before injection into the combustionchamber. The rate of flow of the fuel and oxidizer into the combustioncham- ;ber and the ratio between the two are governed by thecross-sectional areas of the respective injection orifices and thedifferential pressures acting across them. In place of orifices, spraytype injectors can be used.

The liquid fuel, e.g. kerosene, gasoline, benzene or other liquidhydrocarbon fuel, and the liquid oxidizing agent, especially red orwhite fuming nitric acid, are pumped into the combustion chamber wherethey ignite to produce combustion products. The combustion of thesematerials creates a mass of hot, burning gases which are, forciblyejected .at high velocity from the combustio'n chamber through asuitable orifice or nozzle. The reaction from this ejection provides thethrust which propels the rocket. Such motors are of great potentialvalue in assisting the take-off of seaplanes, since additional power isneeded to overcome the skin friction of the water against the hulls ofsuch planes. They are also of "great value in assisting the take-01f ofheavily loaded land planes, since it is well known that only a fractionof the power in a'inodern air plane is used in flight, as compared withthat necessary to lift the plane from the ground under ordinary take-offconditions.

Especially when the rocket is used to assist the takeoff of airplanes,it is of utmost importance for the rocket fuel and oxidizer to igniteimmediately and with certainty, as the plane would almost certainlycrash if the rocket motor failed to fire. For this reason instantaneousignition of the fuel by the oxidizer is essential. With some fuels aslight delay occurs after the reactants mix and before flamingcombustion starts. During this interval additional fuel and oxidizingagents are pumped into the chamber and, when ignition does occur, theaccumulated fuel and oxidizing agents may react explosively. This canresult in damage to the rocket or rigging in which it is supported,other auxiliary equipment or personnel and is wasteful of fuel andoxidant. It is obviously desirable for combustion to start immediatelyonmixing the fuel and oxidiziig agent to atria. ta sirupt, damaging start.Preferably, the ignition delay should be less than about 10milliseconds.

I have found that contacting azines of certain unsaturated aldehydes,e.g. furfuralazine and acroleinazine, with an oxidizing agent, e.g.fuming nitric acid, spontaneously and instantly produces flamingcombustion. Moreover, I have found that a hypergolic system consistingof these compounds can be used to produce instantaneous combustion inreaction motors. Thus, I have found that by arranging the azine in areaction motor combustion chamber so that it is contacted by the firstof an oxidizing agent, e.g. fuming nitric acid, introduced into thechamber spontaneous and instant flaming combustion is produced and theprincipal fuel is thereby instantly ignited. Ignition delay is thusnegligible and smooth starting of the motor is obtained. Thus, areaction propulsion method is provided which is both instantaneous inaction and certain in character so that rocket power failures arereduced to a minimum.

The azines useful as hypergolic agents in my invention are azines ofcertain unsaturated aldehydes, e.g. furfuralazine and acroleinazine.These compounds are readily obtained by the condensation of thealdehydes with bydra'zine. On stirring 2 moles of the liquid aldehydeinto an aqueous solution of 1 mole of hydrazine at ordinarytemperatures, the azine precipitates and is filtered and dried.

. The hypergloic system of my invention is utilizedin reaction motorcombustion systems in any manner suitable to effect contact of thehypergolic agent with the first of the fuming nitric acid introducedinto the combustion chamber. For example, a solution of the hypergolicagent is pumped into the combustion chamber immediately prior to pumpingin the principal fuel using the same means for injection for both.Alternatively, the agent is applied in any suitable manner to the innerwall of the combustion chamber, for example, by blending it with asuitable carrier, e.g. nitrocellulose, so that it can be applied in toform of a film to the wall of the combustion chamber. When applied inthis manner a suspension of .equal weights of the hypergolic agent andthe nitrocellulose dope may be used. Somewhat more or less than thisproportion is also suitable but the proportion of hypergolic agentshould not fall below about 10 percent based on the dope in order to becertain of instantaneous firing. Alternatively, the azine can becompressed with or without minor proportions of a binder into a rod orpellet located in the line of the entering stream of acid. It is anadvantage of my system that no additional mechanical equipment need beadded to the rocket and no change is required in any of its mechanicalfeatures. Thus, the hypergolic agent is introduced into the chamber inone of the manners indicated above and then the agent and enteringstream of fuming nitric acid are contacted or brought together so thatcombustion of the agent "occurs either in the presence of the liquidfuel which has been pumped, usually simultaneously with the acid, intothe chamber or before the liquid fuel is pumped into the chamber.

In one method of performing the process of the present invention, ametal rod is located axially in the head of the combustion chamber andextends into the line of flow of the oxidizer from its orifice. The rod,e.g. a A inch rod, is painted with a mixture of 50 percent ofnitrocellulose lacquer and 50 percent of the hypergolic agent of thepresent invention. As soon as the pump delivers oxidizer to thecombustion chamber it impinges on the hypergolic-nitrocellulosecomposition on the surface of the rod and immediate ignition occurs. Bythis time the principal fuel, for example, gasoline, is also PatentedApr. 12, 1960' impinging on therod and is ignited as soon as it entersthe combustion chamber.

The method of my invention will be further illustrated rby reference to:the :accompanying drawing iwliich is a schematic drawing of a rocketmotor.

:In the drawing the combustion chamber or rocket motor .11 carries in:its head the :threadedmetal 'rod 12 hearing the hypergolic material '13painted :thereon. JROd 12 is arranged axially of combustion chamberll.Fuel :issupplied through line 14 controlled by valveZS through -orifice.15. Oxidizer .is supplied through .line .16 con- :trolled by valve .24and orifice '17. The :orifices "15 and 17 are directed so that thestream offuel. and oxidizer impinge on rod 12. The turbine 18 issupplied with steam :through .line 19 which exhausts through line-20.-Operation of the turbinelS :pumps fuel from1tank21 via --line'l14 tothe combustion chamber and oxidizer 'from tank 22 via line16 to thecombustion chamber.

In operation, turbine 18 pumps :fuel and oxidizer "via 'lines 14 and 16respectively through-orifices 15 :and 17 :so that the streams meet andcontact the 'hypergolic composition 13 on rod 12. Because oftheinstaneoustflaming combustion by the oxidizer of thehypergoliecomposi- --tion, the principal fuel is alsoinstantly ignitedand the :operation begins smoothly.

The ratio of oxidizer to'fuel used willdepend on the itype of fuel andupon the strength of the acid oxidizer used, but in general the ratiosshould be such as'to provide suficient nitric acid to oxidize at leastabout 70 to 80 percent of the fuel. For example, a ratio of 275 'partsof White fuming nitric acid to 100 parts of kero- -sene is satisfactory.The hypergolic agent is used in an :amount sufficient to causeinstantaneous combustion --when contacted by the oxidizer. For example,as little as one gram to as much as ten or more pounds can be --used.

.The amount of hypergolic agent used does not depend 'on the totalamount of fuel and oxidizer to be burned in the rocket motor but on thesize of motor. The hyper- :golic agent is not continuously introducedwith the fuel :and'oxidizer but is introduced before the rocket motor isoperated. After ignition occurs and the rocket motor is in operation, nofurther quantities of hypergolic agent are required so long as therocket motor continues-to operate. Once it is shut off, however, a newsupply of hypergolic agent is introduced before beginning operationagain. Thus the amount of hypergolic agent required bears no relation tothe quantities of fuel and oxidizer eventually consumed but is moreproperly related to the size of the rocket motor. inch in diameter andsix inches in length, as little as one gram of hypergolic agent disposedin the .interiorof the motor may be suflicient when contacted by liquidoxidizer .to elfect instantaneous and flaming ignition. Ina largerrocket proportionately larger quantities of hypergolic agent are used.

'In operation of a reaction motor as shown inthe drawing and having atotal mass of about 50pounds and a In a small rocket motor, for exampleone thrust of 1500 pounds, for example, about one pound of thehypergolic agent in admixture with an equal weight of a nitrocellulosecarrier is applied to the metal rod and kerosene and white fuming nitricacid injected into the combustion chamber under a pressure of about 7pounds per square inch and in a ratio of acid to kerosene ofabout 2.75to l (5.72 pounds per second of nitric acid and 2.08 pounds per secondof kerosene) to impinge on the agent on the rod and produceinstantaneous flaming combustion.

In testingthe hypergolic agents of my invention, about 0.5 ml. of whitefuming nitric acid was placed in a glass thimble measuring 25 'mm. indiameter-and -40 mm. in height. One-half gram of the solid hypergolicagent was added by means of a spatula to thenitric acid. In eachrepetition of the test vigorous and instantaneous flaming occurred,indicating that my hypergolic system provides certain and instantaneousflaming combustion and can be utilized advantageously in reaction motorcombustion systems to-produce smooth starting.

I claim: 1

1. In the combustion of a liquid hydrocarbon fuel ina reaction motorcombustion chamber, the method of instantly initiating the combustion ofthe liquid hydrocarbon fuel which comprises introducing an azineselected from the group consisting of furfuralazine and acroleinazineinto the combustion chamber, contacting the azine "with fuming nitricacid and introducing the liquid hydrocarbon fuel into the combustionchamber.

2. The method of claim v1 in whichthe azine is fur- -furalazine.

3. The method of claim 1 in which the azine is acroleinazine.

4. In the combustion of a liquid hydrocarbon fuel; in a reaction motorcombustion chamber, the method of instantly initiating the combustion ofthe liquid hydrocarbon fuel which comprises introducing an azineselected from the group consisting of furfuralazine and acroleinazineinto the combustion chamber and contacting the azine with fuming nitricacid in close proximity to the liquid hydrocarbon fuel whereby instantcombustion of the fuel is obtained.

5. The method of claim 4 in which the azine isfurfuralazine.

6. The method of claim 4 in which the azine is acroleinazine.

'7. The method of providing a reaction mixture suitable for use ininstantly initiating the combustion of liquid hydrocarbon fuels in areaction motor combustion chamber, which comprises contacting in thechamber an azine selected from the group consisting of furfuralazine.and acroleinazine with fuming nitric acid.

8. The method of claim 7 in which the azine-is furfuralazine.

9. The method of claim 7 in which the azine acroleinazine.

No references cited.

1. IN THE COMBUSTION OF A LIQUID HYDROCARBON FUEL IN A REACTION MOTORCOMBUSTION CHAMBER, THE METHOD OF INSTANTLY INITIATING THE COMBUSTION OFTHE LIQUID HYDROCARBON FUEL WHICH COMPRISES INTRODUCING AN AZINESELECTED FROM THE GROUP CONSISTING OF FURFURALAZINE AND ACROLEINAZINEINTO THE COMBUSTION CHAMBER, CONTACTING THE AZINE WITH FUMING NITRICACID AND INTRODUCING THE LIQUID HYDRO-